Opera checks HTTPS pages to ensure that no internal links are HTTP. Of course, my home page had all my sub-domain links as HTTP relying on the server to redirect to HTTPS. I changed these but still the site was deemed insecure. A little further investigation of the source and there are a couple of links to Cloudflare and Google Fonts that also need changing to HTTPS (because I'm sure Cloudflare and Google will support it) and, at last ...